How resistant cultivars reshape disease management: An application to citrus greening disease

CONTEXT According to the FAO, crop diseases cause about $220 billion in losses each year, and the development of disease-resistant cultivars is one potential long-term solution to combat such losses. However, limited research has considered disease-resistant cultivar adoption in the context of perennial cropping systems, where the crop is not replanted at the end of each season. OBJECTIVE We use citrus greening disease as a case to demonstrate how the perennial nature of a crop can affect the timing of adopting resistant cultivars, and further identify the threshold of resistance efficacy at which growers will stop using active chemical control of the insect vector of the disease. METHODS We model the decision of when to adopt a resistant cultivar when they become available and whether and when to discontinue psyllid control using a dynamic bioeconomic model. A baseline scenario without resistant cultivars is compared to scenarios with ten resistance levels, from imperfect to perfect. RESULTS AND CONCLUSIONS Through simulations, we determine that the optimal timings of adopting the new cultivar and discontinuing chemical vector control vary, as a function of efficacy level, grove density, and tree age. Furthermore, we identify a resistance efficacy threshold of 90% as a critical turning point, beyond which it becomes optimal for all growers, regardless of grove age, to cease insecticide spraying prior to adopting resistant cultivars. Additionally, we find that for any given efficacy level, adoption timing varies, which could lead to spatial externalities. SIGNIFICANCE This forward-looking study informs decision-making regarding resistant cultivars, emphasizing the need to address disease management in the absence of full resistance. Variations in growers' decisions may cause negative externalities, complicating the transition to resistant cultivars in perennial systems. • Disease-resistant cultivars reshape disease management. • Model shows adoption of resistant cultivars in perennial cropping systems may be delayed due to the perennial nature. • Resistance efficacy threshold is identified for permanently stopping vector control in citrus greening. • Variations in adoption timing and vector control may result in negative externalities.